1. Field of the invention
The present invention relates to a magnetic recording disk, and more particularly to a magnetic recording disk which is improved in both the electromagnetic conversion characteristics and the rotational properties.
2. Description of prior arts
A magnetic recording disk has been recently employed as a recording medium for a computer or a word processer. With the practical use of an electronic camera in recent years, the magnetic recording disk (i.e., magnetic sheet disk) of small size is standardized and has been employed as a recording medium for the electronic camera.
The magnetic recording disk basically comprises a nonmagnetic support and two magnetic recording layers provided on both surfaces of the support, and has a similar construction of layers to that of a magnetic recording medium in the form of tape (i.e., a magnetic recording tape) from the viewpoint that one of the magnetic recording layers is provided on the nonmagnetic support. However, as for various properties such as the running (i.e., rotational) properties, the magnetic recording disk is much highly required as compared with the magnetic recording tape.
In more detail, as for the magnetic recording disk, a magnetic head runs repeatedly on the same surface of the disk in contact with the surface of the disk to regenerate information. While the magnetic recording tape is kept in contact with the magnetic head by providing a certain level of tension to the tape, the recording disk is rotated under pressing the surface thereof against the magnetic head to record and regenerate information. Accordingly, the contact conditions between the disk and the magnetic head largely depend upon a flexural stiffness (flexural strength) of the magnetic recording disk. From the viewpoint of satisfactory contact between the disk and the magnetic head, the flexural stiffness of the disk preferably is high. However, if the flexural stiffness is too high, the magnetic head is harshly abraded and at the same time, the magnetic recording layer is liable to be damaged. Particularly, a variety of materials of the magnetic head have been developed recently, and a magnetic head using a material having low hardness such as a sendust head has been employed in place of a conventional ferrite head. In the case of using such magnetic head, the above-mentioned drawbacks are prominently observed.
At present, recording media are under requirement for increase of the recording density, and this requirement is also applied to the magnetic recording disk. Moreover, the magnetic recording disk needs to be further improved in the electromagnetic conversion characteristics as compared with a magnetic recording tape.
Since the magnetic sheet disk especially for an electronic camera or for a device of converting a photographic silver halide image to electromagnetic information is required to show high resolution almost the same as that of the conventional photography using silver salt, the electromagnetic conversion characteristics thereof are particularly required to be highly enhanced.
As a measure for improving the elctromagnetic conversion characteristics of the magnetic sheet disk for an electronic camera, Japanese Patent Provisional Publication No. 58(1983)-122623 proposes a magnetic sheet disk using a ferromagnetic metal powder as magnetic powder and being provided with a magnetic recording layer on a support of smaller thickness than that of the conventional disk. The ferromagnetic metal powder shows excellent electromagnetic conversion characteristics, and hence it is suitable as a magnetic powder to be employed for a magnetic sheet disk for use in an electronic camera or in the image conversion device.